(1) Field of the Invention
The present invention relates to a catalyst which comprises a catalytically active amount of at least one oxygen-containing molybdenum and/or tungsten compound on an oxidic support material and has been calcined at from 400° C. to 900° C. after application of the precursor compounds of the catalytically active compounds to the support material or a support material precursor, and to a process for preparing it. This catalyst is used in processes for preparing polytetrahydrofuran, tetrahydrofuran copolymers and diesters or monoesters of these polymers.
Polytetrahydrofuran, hereinafter referred to as PTHF for short, which is also known as polyoxybutylene glycol, is used as a versatile intermediate in the plastics and synthetic fibers industries and is employed, inter alia, for producing polyurethane, polyester and polyamide elastomers. In addition, it is, possibly in the form of its derivatives, a valuable auxiliary in a variety of applications, e.g. as dispersant or in the deinking of waste paper.
Industrially, PTHF is advantageously prepared by polymerization of tetrahydrofuran over suitable catalysts. Additional reagents whose addition makes it possible to control the chain length of the polymer chains and thus to set the mean molecular weight to the desired value are used in this process. Such chain termination reagents are also known as “telogens”. The chain length is controlled via selection of type and amount of telogen. Choice of suitable telogens additionally makes it possible to introduce functional groups at one end or at both ends of the polymer chain. For example, use of carboxylic acids or carboxylic anhydrides as telogens makes it possible to prepare the monoesters or diesters of PTHF. Other telogens act not only as chain termination reagents but are also incorporated into the growing polymer chain of PTHF and have the function of both a telogen and a comonomer. Examples of such comonomers are telogens having two hydroxy groups, for example dialcohols. Examples of such dialcohols are ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, 2-butyne-1,4-diol, 1,6-hexanediol or low molecular weight PTHF. The use of such comonomers leads to tetrahydrofuran copolymers. In this way, the PTHF can also be chemically modified. An example is the use of the telogen 2-butyne-1,4-diol whose addition leads to the presence of a proportion of C—C triple bonds in the polymer chains of the PTHF. PTHF which has been modified in this way can be further modified chemically at these points due to the reactivity of these triple bonds, e.g. by hydrogenation of the triple bonds to form double bonds, by subsequent grafting of other monomers to adjust the properties of the polymer, crosslinking to form polymers having a comparatively rigid structure or other customary measures of polymer chemistry. Complete hydrogenation of the triple bonds present is likewise possible and generally leads to PTHF having a particularly low color number.
Industrially, the preparation of PTHF is predominantly carried out by two-stage processes in which tetrahydrofuran is, for example, polymerized in the presence of fluorosulfonic acid to form PTHF esters which are subsequently hydrolyzed to give PTHF. In a further two-stage process, tetrahydrofuran is polymerized with acetic anhydride in the presence of acid catalysts to form PTHF diacetate which is subsequently transesterified with methanol to give PTHF.
Apart from the fact that a two-stage process has to be carried out, a particularly disadvantageous factor is that by-products such as hydrofluoric acid or methyl acetate are formed.
Single-stage processes for preparing PTHF in which tetrahydrofuran is polymerized using diols, water or low molecular weight PTHF as telogen over acid catalysts are also known. The catalyst or the catalyst system can be homogeneous, i.e. present in solution in the reaction system, or it is possible to use heterogeneous, largely undissolved catalyst systems.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98.
DE-A-44 33 606 describes a process for preparing PTHF, PTHF diesters of C2-C20-monocarboxylic acids or PTHF monoesters of C1-C10-monocarboxylic acids by polymerization of tetrahydrofuran over a heterogeneous catalyst in the presence of one of the telogens water, 1,4-butanediol, PTHF having a molecular weight of from 200 to 700 dalton, a C1-C10-monocarboxylic acid or a carboxylic anhydride of a C2-C20-monocarboxylic acid or a mixture of these telogens, where the catalyst is a supported catalyst comprising a catalytically active amount of an oxygen-containing tungsten or molybdenum compound or a mixture of these compounds on an oxidic support material and has been calcined at from 500° C. to 1000° C. after application of precursor compounds of the oxygen-containing molybdenum and/or tungsten compounds to the support material precursor.
DE-A-196 41 481 discloses a process for preparing polytetrahydrofuran, copolymers of tetrahydrofuran in 2-butyne-1,4-diol, diesters of these polymers with C2-C20-monocarboxylic acids or monoesters of these polymers with C1-C10-monocarboxylic acids by polymerization of tetrahydrofuran in the presence of one of the telogens water, 1,4-butanediol, 2-butyne-1,4-diol, polytetrahydrofuran having a molecular weight of from 200 to 700 dalton, a C1-C10-monocarboxylic acid or a carboxylic anhydride of a C2-C20-monocarboxylic acid or a mixture of these telogens over a heterogeneous support catalyst. The supported catalyst comprises a catalytically active amount of an oxygen-containing molybdenum and/or tungsten compound on an oxidic support material and has been calcined at from 500° C. to 1000° C. after application of precursor compounds of the oxygen-containing molybdenum and/or tungsten compounds to the support material precursor and activated by treatment with a reducing agent before being used as polymerization catalyst.
It is an object of the present invention to provide a catalyst which has a higher activity than the known catalysts so as to achieve higher polymer yields and/or space-time yields.